multi battery approach - so crazy it might work?

[BillyTungsten]

All right... I have spent enough time lurking! I need some input from you guys before I burn down / blow up something with this idea.
I recently picked up a 1973 K5 (flew one-way from MN to CO to get it, drove it back without a hitch) I am new to K5's, and I must say: I LOVE THIS TRUCK!

Anyway, here is the scoop: I have these pieces sitting in the garage left over from an electric boat project:

(2) AGM dual-purpose (crank & cycle) group 30 Batteries
(1) three bank, 30 amp on-board marine battery charger
(1) Perco marine battery isolater / combiner switch

all components are nearly brand new, and I know from experience these batteries are strong and the charger suits them very well.

.. so I just picked up a 1500 watt inverter, and got to thinking.... or did I get to thinking and then pick up the inverter? Doesn't matter.

Run the alternator to the inverter, inverter to the marine charger, and charger of course to the two AGM batteries... normal operation would have the alternator charging the existing vehicle battery while also supplying juice to the inverter which is charging / maintaining the AGMs.

To use 110 power on the trail, I would turn off (I think) the charger, flip the perko switch to bring the AGM's (instead of the alternator) onto the supply side for the inverter, and whammo! Fire up the blow dryer or the disco ball or whatever.

I know I'm nuts, but I need to know: am I crazy? This is nearly a thousand bucks worth of goodies and I would rather use them for something other than holding the garage door open when I'm carrying in groceries.

Thanks!

 

[Blue85]

I'm not really familiar with the batteries you are describing. Are they all 12V batteries? Is there any reason they can't be charged directly from the alternator? There's no reason why you can't use the power inverter to run 110VAC stuff. You may need more alternator, though, if you are charging multiple batteries and running additional equipment.

What kind of charge does the marine charger provide?

 

[BillyTungsten]

The batteries are Marine deep-cycle batteries normally used for trolling motors. AGM is Absorbed Glass Mat - a really cool way to construct the guts to keep things together under stress (heat, cold, vibe, inversion, etc). Optimas use a different approach to solve the same problems, and compete with these batteries in the marine arenas...
Yes, 12 volt. Group 30 is large. about 87 pounds apiece...

Yes, theoretically they could be charged off of the alt... but they can be sensitive... and they are not cheap. Dunno if I would foul things up by trying... and I really like the idea of the system being able to be 100% isolated from the vehicle electrical system...

The type of charge? 30 amp total, distributed dynamically across three banks (I would only use two). Also will float / maintain the batts.

One cool thing is that AGMs only create about 5% resistance to charging... common lead-acid is closer to 30%... and that is energy lost.

 

[scrappy88]

Keep in mind though you are losing energy converting dc to ac back to dc to charge the batteries. I think a better option would be a isolator/combiner and have the alt charge all of the batteries.

Check out www.hellroaring.com they have some nice isolators plus plenty of diagrams on different setups. One looks similar to what you want to do. Look in the RV/Towing section, they have a setup to isolate a house battery bank from the main vehicle battery and still keep everything charged.

 

[BillyTungsten]

huh. Good point.

I will check the hellroaring stuff...

 

[BillyTungsten]

I have looked at hellroaring, in recent weeks and then again tonight... it sounds like really nice stuff but it I would like to avoid the $ if possible. It is interesting that they make this comment regarding the RV / Trailer system: "...(Don't be fooled by low cost battery disconnect devices as a solution. If you try to use these, your starting battery will get deep cycled and will result in early failure.) "
I wonder if that means I could have trouble if I did try to simply charge all three batts w/ the alt... especially since I'm not yet sure what sort of alternator it is... it looks rather 'normal' in size... I do not know how to tell the output, I should have looked closer for some labeling, I guess ;-)

The efficiency loss in the dc/ac/dc conversion is a good point... I do not know how much of an impact that would have. A good reason to do a little more research!

One of the things that appealed to me about using the marine charger is the cable runs... the runs between the inverter and the batts need to be beefy, and I have #2 for that, but the runs from the charger to the batts are about the thickness of a light duty extension cord... not a big deal, but a bit less $.

I envision a control panel on one of the diamond plate toolboxes in the bed (I installed the boxes this week) with two marine voltmeters, one for each battery, the marine isolater / combiner switch, two outdoor style covered 110 volt plugs, a couple 12 volt outlets, and an amp meter to show the realtime draw on the system... I admit that this is all affected somewhat by building boats and liking the marine equipment for its reliability and toughness.

hmmm....